Evolution of microstructure and microsegregation in Ni-Mn-Ga alloys directionally solidified under axial magnetic field

Highlights: • The magnetic field reduced the microsegregation during directional solidification. • The magnetic field refines cells/dendrites during directional solidification. • The magnetic field induced convection is investigated by a numerical simulation. In this work, the microstructure and microsegregation in Ni-Mn-Ga alloys directionally solidified using a seedless Bridgman technique under an axial magnetic field are investigated. The experimental results indicate that the magnetic field refines cells/dendrites and reduces microsegregation. A numerical simulation is performed to investigate convection during directional solidification under an axial magnetic field. Thermoelectric magnetic convection at the cell/dendrite scale is found to be primarily responsible for the refinement of cells/dendrites and for the inter-cellular/dendritic composition homogeneity under a magnetic field. This finding is of significance as it highlights the role of magnetic field on the microsegregation during directional solidification, which could be used in future as a tool for controlled microstructure growth.